I would be concerned with the health and well-being of the conures if left with Sennie. Sennies tend to be jealous/territorial and would probably inflict damage on the conures if given the opportunity. Thus the scenario IF you got the sennie would be that you would have to alott separate training times/alone times with each. Do you have the time required?
BTW all birds will bite if frightened, especially if they are clipped and have no flight ability to avoid "danger".
I would also read up as much as you can about

traits/agression issues before making your decision. As mentioned many times on this forum, sennies are very manipulative parrots. Meaning if you dont control them they will CONTROL you! So read, read, read, and read some more.
You need to look at every possible outcome and assess your personal situation.
Wayne